// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/disk_cache/blockfile/file_lock.h"

#include "base/atomicops.h"

namespace {

void Barrier()
{
#if !defined(COMPILER_MSVC)
    // VS uses memory barrier semantics for volatiles.
    base::subtle::MemoryBarrier();
#endif
}

} // namespace

namespace disk_cache {

FileLock::FileLock(BlockFileHeader* header)
{
    updating_ = &header->updating;
    (*updating_)++;
    Barrier();
    acquired_ = true;
}

FileLock::~FileLock()
{
    Unlock();
}

void FileLock::Lock()
{
    if (acquired_)
        return;
    (*updating_)++;
    Barrier();
}

void FileLock::Unlock()
{
    if (!acquired_)
        return;
    Barrier();
    (*updating_)--;
}

} // namespace disk_cache
